The present invention relates generally to a communication system design, and more particularly to a method and system for adjusting receiver gain and monitoring signal strength in telecommunication systems where the transmission and receive periods are interleaved.
A telecommunication system typically includes communication equipments on two ends of the communication link. For example, on one end, a base station is set up to communicate with, on another end, one or more mobile terminals traveling in a cell. Information is received and transmitted by both the base station and the mobile terminals. Both the base station and the mobile terminal have radio receiver circuitries that process incoming signals. Managing the signal gain is an important aspect of the function of these receiver circuitries.
In many radio receivers, a gain controller circuit is used to control the input signal to the receiver, because the input signal strength typically varies dramatically due to the change of environment or the signal characteristics. For example, the input signal strength can vary, due to a fading channel, more than 10 dB within a few milliseconds. Since a dynamic range of the receiver is limited, it cannot handle a wide dynamic range of input signal. Any signal beyond the dynamic range of the receiver circuit will be rejected as noise. A main purpose of installing a gain controller circuit on the receiver path is to reduce the gain of the receiver when the input signal strength is too high, and to increase the gain when the input signal strength is too low, so that the signal strength is kept almost at an optimized level within the receiver's achievable dynamic range.
Since the received signal strength varies rapidly, the gain control mechanism has to be dynamic as well to track the change thereof. In method is to let the gain controller continuously monitor the received signal strength (RSS) and adjust the receiver gain according to the most recent RSS value. However, this continuous RSS monitoring and gain adjustment is not possible for communication systems using Time Division Duplex (TDD) or half duplex Frequency Division Duplex (FDD) technologies where time slots for receive and transmit are interleaved.
In a typical TDD or half duplex FDD communication system, radio channels are divided by code sequences and time periods, but information transmitted and received are carried on the same frequency. Separate time slots are assigned for transmit and receive, and multiple time slots may be assigned to allow different data transmission rates for the downlink and uplink communications.
For the initial gain setting of each receive period in TDD systems, one has to rely on the outdated RSS value of the last receive period. This will result in an inaccurate initial gain setting since there could be a major difference between the RSS values of two receive periods as they are separated in time, especially when there is a fast channel fading. In other words, if the RSS of the last receive period is relied on, there is a high possibility that the received signal is out of the receiver dynamic range at the beginning of each receive period in TDD systems, thereby resulting in a high packet error rate. For example, assuming that a 10 ms TDD frame has 5 ms for receive and 5 ms for transmit, the distance change in 5 ms, given a traveling speed of 60 km/h, will be approximately 0.14 m, which is more than 1 wavelength in distance (0.12 m) in the 2.6 GHz band, and is thus beyond the coherent distance of a fading channel.
For these reasons, it is desirable to design a new method and system for minimizing the discontinuity effect of the received signal strength monitoring and for adjusting receiver gain in TDD systems more accurately for establishing better communication quality of the telecommunication system.